1. Field of the Invention
The invention is directed to the field of micromachined gyroscopes, and in particular to designs and methods with inherent disturbance-rejection capabilities.
2. Description of the Prior Art
With the advances in micromachining technologies, low cost, on-chip inertial micro-sensors are beginning to enter the market. Derived from the conventional integrated circuit (IC) fabrication technologies, micromachining processes allow mass-production of microstructures with moving bodies on a chip together with control and signal conditioning electronics. Thus expensive and bulky conventional inertial sensors will be eventually replaced by their micromachined counterparts without compromising performance. Likewise, micromachined gyroscopes could potentially provide high accuracy rotation measurements leading to a wide range of applications including navigation and guidance systems, automotive safety systems, and consumer electronics. Gyroscopes are probably the most challenging type of transducers ever attempted to be designed using MEMS technology. Due to complexity of their dynamics, the current state of the art micromachined gyroscopes require an order of magnitude improvement in performance, stability, and robustness.
All existing micromachined rate gyroscopes operate on the vibratory principle of a single proof mass suspended by flexures anchored to the substrate. The flexures serve as the flexible suspension between the proof mass and the substrate, making the mass free to oscillate in two orthogonal directions—the drive and the sense as shown in simplified diagram of FIGS. 3a and 3b. 
The proof mass is driven into resonance in the drive direction by an external sinusoidal force with a certain drive frequency. If the gyroscope is subjected to an angular rotation, the Coriolis force is induced in the y-direction. The resulting oscillation amplitude in the sense direction is proportional to the Coriolis force, and thus to the angular velocity to be measured.
To achieve the maximum possible gain, the conventional gyroscopes are designed to operate at the peak of the response curve. This is typically achieved by matching drive and sense resonant frequencies as shown in the graph of FIG. 3c. However, the system is very sensitive to variations in system parameters causing a shift in the resonant frequency. For example, a 1% fluctuation in frequency matching between drive and sense modes will produce an error of 20% in the output signal gain. Under high quality factor conditions the gain is high, however the bandwidth is extremely narrow. In addition, the gain is affected significantly by fluctuations in damping conditions as depicted in FIG. 2b. 
Fabrication imperfections are inevitable, and affect material properties and geometry of MEMS structures. For surface micromachining, the thickness of the suspension elements is determined by deposition process, and the width is affected by etching process. In addition, Young's Modulus of the structure is affected by deposition conditions. Variations in elastic modulus, beam thickness or residual stresses have drastic effects on resonant frequencies of gyroscopes. Generally, very sophisticated control electronics is used to provide operation in the region of the resonance peak. Furthermore, during the operation time of these devices, fluctuations in the ambient temperature alter the gyroscope geometry together with structural properties, and pressure fluctuations affect the damping conditions, resulting in significant errors.
To eliminate the limitations of the existing micromachined gyroscopes, what is needed is a design approach which avoids these limitations of the prior art.